The present invention relates to an improvement of the head of a drilling tapping screw for use in fastening steel plates together so that it may drill a starting hole to execute tapping and fastening operation. This specific improvement may be applied to other every kind of screw heads.
Fig.14 shows a conventional drilling tapping screw with a hexagonal head, (A) being a plan view and (B) a front view.
Said conventional drilling tapping screw comprises a hexagonal head 50, and a shank 51 extending downward from the head 50 and having a drilling portion 52 on its lower end. A tapping and fastening thread 53 is formed on shank 51 so as to extend from the basal part of said drilling portion 52 toward the head 50. This particular drilling tapping screw is used in securely fastening metallic plates such as steel plates together, or fastening others object to such a metallic plate, so that said drilling portion 52 may drill a starting hole in the metallic plate through the other object, while its thread 53 chases a female screw thread in the starting hole as it fastens the object to the plate at the same time.
The head 50 of said drilling tapping screw may be of pan, oval, or hexagonal shape, and, in general, has a slotted or cross-recessed groove thereon.
A rotary fastening tool may be engaged with this head 50 to provide a driving force to the head 50, thereby driving the screw into the metallic plate.
As mentioned above, this drilling tapping screw is widely used to firmly fasten metallic plates to each other, or to fasten a metallic plate to an object made from another material. For example, the screw may be utilized in the construction of steel houses which are now opening a market in the housing industry. The steel house is built by means of a framing method using galvanized steel members with a thickness of around 1mm. The framework is, of course, constituted by steel products. To firmly fasten together such steel products to constitute a framework, drilling tapping screws are used.
FIG. 15 illustrates fastened frame members for a steel house. As shown in FIG. 15(A), stud members 56 used as stanchions are vertically spaced on a track member 55, with the stud members 56 and track members 55 being securely joined by drilling tapping screws 60. The upper portions of the stud members 56 are not shown for simplicity.
FIG. 15(B) is an enlarged view showing the track member 55 and the stud member 56 securely fastened together from opposite sides thereof, with the head of the drilling tapping screw 60 sticking out of the track member 55.
A wallboard 70 such as plasterboard is, for example, joined to this framework, and then, securely fixed to the frame by a drilling tapping screw 61.
FIG. 15(C) is a plan view illustrating the wallboard 70 fastened to the framework for a steel house.
After fastening the stud member 56 to the track member 55 with the drilling tapping screws 60, the wallboard 70 may inevitably rise and get wavy at a site where the head of the drilling tapping screw 60 is positioned, depending on the size or thickness of the head, as illustrated.
FIG. 16 is an enlarged view illustrating a wallboard 70 fastened to a framework. This shows the result of a process comprising firmly fastening a track member 55 to a stud member 56 by means of a drilling tapping screw 60, then joining the wallboard 70 to this frame using another drilling tapping screw 61. As apparent from this figure, the wallboard 70 rises at a site where the head 50 of the drilling tapping screw 60 is placed.
It appears that in order to avoid such a rising or waving in the wallboard, decreasing the thickness of head 50 can solve the above problem, but a thinner head requires formation of a cross-shaped groove thereon so that the head may receive a driver bit defining a tip engaging portion of rotary fastening tool. Also, the formation of cross-shaped groove decreases the screw head strength, so that the screw head may torn off when the drilling tapping screw is driven by the rotary fastening tool.
Therefore, the present invention has a primary task of totally eliminating any waving or rising phenomenon of the wall-board which may inevitably occur in fastening the wallboard etc. to the steel framework by the use of the above-described conventional drilling tapping screws.
Thus, an object of the present invention is to totally prevent different plates joined to the surface of a frame from rising or getting wavy because of the head of the drilling tapping screw which may stick out from said frame after fixing together the metallic frame members with the drilling tapping screw.
On the other hand, it is a further object of the present invention to provide a drilling tapping screw having a high-strength head regardless of its shape thereof during the fastening operation.
It is also another objective of the present invention to enable temporary locking of a wallboard on a frame in advance of fixing the wallboard to the frame in the construction of steel house.
That is, if the screw head is arranged in a shape so that it may stab through the wallboard, the head of a drilling tapping screw intended for fixing the framework can also temporarily lock the wallboard in advance with a site thereof to ensure that the subsequent fixing operation for the wallboard will be easily carried out by a drilling tapping screw.
Thus, it is another objective of the present invention to make a screw head in so a specific shape that it may temporarily lock the plate being joined to the screw head. Furthermore, this temporary locking function not only temporarily locks the wallboard on the frame but also result in fixing the wallboard at both its front and back sides, which increases the fixing strength as well as resistance to quakes in prefabricated buildings such as said steel houses.
The present invention has been made to improve the head of the drilling tapping screw in the above-mentioned manner, and can be adapted to all types of screw heads.